(1) Field of the Invention
The present invention relates to a piston for an engine.
(2) Description of Related Art
Conventionally, as shown in FIG. 6, a piston for an engine having a resin coating film 102 and a recess 103 on a surface of a skirt part 101 is known.
According to this kind of piston, a profile of the skirt part 101 is optimized by the resin coating film 102, and there are obtained advantages of reducing slapping noise of the piston and friction of the skirt part 101 by engine oil stored in the recess 103.
However, in the conventional technique, as shown in FIG. 6, since the plurality of recesses 103 are discretely arranged in spots on the single resin coating film 102, a friction reducing function of the engine oil for the skirt part is insufficient.
In other words, as shown in FIG. 6, since the plurality of recesses 103 are discretely arranged in spots on the single resin coating film 102, the recess 103 is surrounded by the resin coating film 102 and therefore it is difficult to supply the engine oil to the recess 103. Thus, a sufficient amount of the engine oil is not held in the recess 103 and therefore the friction reducing function of the engine oil for the skirt part 101 is insufficient.